Fibrous filtration face mask having corrugated polymeric microfiber filter layer

Abstract

A composite structure contains a lofty corrugated nonwoven web of polymeric microfiber that is maintained in a corrugated condition by securing a fabric to the corrugated web at the valleys of the corrugations. The composite structure is made without substantially effecting web loft by (i) introducing the nonwoven web to the ends of a plurality of spaced paddles, (ii) causing the spacing between the ends of the paddles to decrease to corrugate the nonwoven web, and (iii) securing the fabric to the corrugated nonwoven web at the valleys of the corrugations. A composite structure of this construction made by this method provides very good filtration performance, making it particularly suitable for use as a filter in a cup-shaped face mask. The composite structure also is very suitable for use as thermal insulation in apparel.

What is claimed is: 
     
       1. A fibrous-filtration-face-mask that comprises: a cup-shaped fluid-permeable mask body that fits over the nose and mouth of a person, the cup-shaped fluid-permeable mask body comprising a corrugated nonwoven web of polymeric microfiber as a filter layer, the corrugated nonwoven web of polymeric microfiber having a plurality of corrugations that follow an approximately sinusoidal path when viewed from a side-elevation where adjacent side walls of the corrugations do not make substantial contact with each other, there being a means for retaining the corrugated shape of the nonwoven web of polymeric microfiber secured to valleys of the corrugations such that the shape-retaining means is not coextensive with the nonwoven web of polymeric microfiber.   
     
     
       2. The fibrous-filtration face mask of claim 1, wherein the corrugated nonwoven web of polymeric microfiber is secured to the shape-retaining means by intermittent securement points. 
     
     
       3. The fibrous-filtration face mask of claim 2, wherein the intermittent securement points are spaced by a distance Y and are offset from securement points on an adjacent valley by a distance of about 1/2Y, where Y is in the range of 0.5 to 5 cm. 
     
     
       4. The fibrous-filtration face mask of claim 2, wherein the securement points occupy less than 5 percent of the corrugated surface area. 
     
     
       5. The fibrous-filtration face mask of claim 2, wherein the securement points occupy less than 2 percent of the corrugated surface area. 
     
     
       6. The fibrous-filtration face mask of claim 1, wherein the nonwoven web of polymeric microfiber and the shape-retaining means have a corrugation ratio of 10:1 to 1.2:1. 
     
     
       7. The fibrous-filtration face mask of claim 1, wherein the nonwoven web of polymeric microfiber and the shape-retaining means have a corrugation ratio of 5:1 to 1.5:1. 
     
     
       8. The fibrous-filtration face mask of claim 1, wherein the nonwoven web of polymeric microfiber has an arithmetic median fiber diameter of less than about 10 micrometers. 
     
     
       9. The fibrous-filtration face mask of claim 1, wherein the nonwoven web of polymeric microfiber has a arithmetic median fiber diameter in the range of 2 to 8 micrometers. 
     
     
       10. The fibrous-filtration face mask of claim 1, wherein the average pore size of the corrugated nonwoven web of polymeric microfiber is less than about 150 μm. 
     
     
       11. The fibrous-filtration face mask of claim 1, wherein the average pore size of the corrugated nonwoven web of polymeric microfiber is about 10 to 100 μm. 
     
     
       12. The fibrous-filtration face mask of claim 1, wherein the corrugated nonwoven web of polymeric microfiber comprises 80 weight percent polymeric microfiber, based on the weight of the fibrous material. 
     
     
       13. The fibrous-filtration face mask of claim 1, wherein the corrugated nonwoven web of polymeric microfiber comprises approximately 100 weight percent blown microfiber based on the weight of the fibrous material. 
     
     
       14. The fibrous-filtration face mask of claim 1, wherein the corrugated nonwoven web of polymeric microfiber comprises electrically-charged microfiber that contains polypropylene. 
     
     
       15. The fibrous-filtration face mask of claim 1, wherein there are a plurality of corrugated nonwoven webs of polymeric microfiber secured to the shape-retaining means. 
     
     
       16. The fibrous-filtration face mask of claim 1, wherein the shape-retaining means is a fluid-permeable fabric that is intermittently secured to the corrugated nonwoven web of polymeric microfiber by ultrasonic welds. 
     
     
       17. The fibrous-filtration face mask of claim 1, wherein the corrugated nonwoven web of polymeric microfiber provides the face mask with an effective surface area of at least 1.3 times an effective surface area of a face mask that has a non-corrugated filter and is of substantially the same size. 
     
     
       18. The fibrous-filtration face mask of claim 1, wherein the corrugated nonwoven web of polymeric microfiber provides the face mask with an effective surface area of at least 1.6 times an effective surface area of a face mask that has a non-corrugated filter and is of substantially the same size. 
     
     
       19. The fibrous-filtration face mask of claim 1, wherein there is about 8 to 20 millimeters of corrugated nonwoven web of polymeric microfiber between two adjacent valleys.